1. Field of the Invention
The present invention relates to an ion production device and an ion beam irradiation apparatus for carrying out a process of implanting ions into a substrate by irradiating the substrate with an ion beam. More particularly, the invention relates to improvement of means for suppressing the accumulatively charging (charge-up) of the substrate when it is irradiated with the ion beam. The charge-up is used hereinafter as the accumulatively charging.
2. Description of the Related Art
There is a proposal of suppressing the charge-up of the substrate when it is irradiated with ion beam. Plasma produced from a plasma production device is supplied in a vicinity of the substrate. Electrons included in the plasma are used of neutralizing the positive charge produced by the ion beam irradiation. The proposed technique supplies to the substrate electrons with lower energy, when comparing with the technique utilizing secondary electrons emitted from an object when it is hit with electrons emitted from the filament. Accordingly, the proposed technique has an advantage of reducing the negative charge in the substrate.
A plasma production device of the radio frequency discharge type is the plasma production device using the radio frequency discharge for plasma generation. This type of the plasma production device is advantageously featured in that a) the lifetime is long because there is no filament, and b) it is operable at low gas pressure. When comparing with the plasma production device of the type which uses the filament for the discharge.
A sectional view showing the related art of a ion beam irradiation apparatus which is provided with a plasma production device of the radio frequency discharge type, is shown in FIG. 9.
An ion beam 2, which is shaped like a spot in cross section, is extracted from an ion source (not shown) in the ion beam irradiation apparatus. And it necessary, the ion beam is mass separated and accelerated before introducing in a vacuum chamber 8. In a vacuum chamber (process chamber) 8, the ion beam is irradiated onto a substrate (e.g., a semiconductor substrate) 4 held by a holder 6 so as to implant ions in the substrate 4 (ion implanting process), while being reciprocatively scanned in fixed directions X by the magnetic field (perpendicular to the surface of the drawing sheet of the figure, e.g., horizontal directions, which will be used hereinafter for the fixed directions).
The substrate 4 and the holder 6 are reciprocatively moved by a holder drive device 10 in a direction Y (e.g., vertical direction, which will he used hereinafter for the direction) The direction Y is substantially perpendicular to the directions X. This reciprocal scanning operation cooperates with the scanning of the ion beam 2 (hybrid-scan) to uniformly irradiate the entire surface of the substrate 4 with the ions.
A plasma production device 20 of the radio frequency discharge type is provided in the vicinity of the substrate 4 as viewed in the beam stream moving direction. The plasma production device 20 produces plasma 12 and supplies it to a region near to and in the vicinity of the substrate 4, whereby suppressing the charge-up of the surface of the substrate 4. The charging up is occurred by the irradiation of the ion beam 2.
The plasma production device 20 is provided with a cylindrical plasma production chamber 22. Gas 16 is introduced into the cylindrical plasma producing chamber 22. An antenna 28 radiates radio frequency wave 18 into the gas-contained chamber, so that the gas is ionized to produce plasma. The produced plasma is emitted outside through a plasma emission hole 24.
A magnetic coil 26, which is provided outside the plasma producing chamber 22, produces a magnetic field into the plasma producing chamber in the direction along an axis 23, which passes through the center of the plasma emission hole 24. The magnetic field is used for producing and maintaining the plasma 12.
When the substrate 4 is irradiated with the ion beam 2, the surface of the substrate 4 is positively charged with the positive charge of the ion beam 2. In particular, when the surface is made of insulating material, it is easy to be charged. When the ion beam is irradiated, the plasma 12 is supplied to a region near the substrate 4 as described above, electrons in the plasma 12 are attracted to the surface of the positively charged substrate, thereby neutralizing the positive charge. If the positive charge is neutralized, the attraction of the electrons into the substrate 4 automatically stops as taught by the theory. In this way, the positively charging up of the substrate surface by the ion beam irradiation is suppressed.
With presence of the plasma production device 20 constructed as mentioned above, the charging up of the substrate surface, which results from the ion beam irradiation, may be suppressed to a certain extent. However, the suppression of the substrate surface charging up is unsatisfactory for the following two reasons.
1) For the scanning, the ion beam 2 is moved in the X direction as described above. The plasma 12 is merely emitted through the small plasma emission hole 24 of the plasma production device 20. Accordingly, an amount of plasma 12 supplied to the ion beam 2 when the ion beam 2 scans a region near the plasma emission hole 24 is greatly different from the plasma amount when the ion beam 2 scans a region located apart from the plasma emission hole 24. This fact implies that it is difficult to uniformly supply the plasma 12 to a region near the ion beam being moved for scan. Accordingly, the suppression of the charge-up is non-uniform. As a result, the charged voltage difference is created on the entire surface of the substrate 4, which receives the ion beam 2 being moved for scan. And the charged voltage is high at some locations on the substrate surface. Actually, the ion beam 2 includes not only ions but also electrons gathered from its environment so that the ion beam 2 is in a plasma state. This is called xe2x80x9cbeam plasmaxe2x80x9d.
2) The electrons in the plasma 12 produced from the plasma production device 20 have an energy distribution, which is called a Maxwell-Boltzman distribution. The electrons in the plasma 12 produced from the plasma production device have peaks at several eV in the Maxwell-Boltzman distribution of the electrons. Some of those electrons have energy much higher than the peak energy (e.g., 10 to 20 eV or higher). When the substrate 4 receives the electrons having such high energy in a state that the substrate 4 is not irradiated with the ion beam 2, the substrate 4 is negatively charged by the high energy electrons. And the charged voltage on the substrate surface increases to a voltage corresponding to the energy of the high energy electrons.
Generally, in the plasma production device 20 of the radio frequency discharge type, electrons are easy to be accelerated by the radio frequency electric field. Accordingly, high energy electrons are easy to be produced. When an ECR (electron cyclotron resonance) discharge, as is the kind of radio frequency discharge is applied, the electrons are more accelerated by the electron cyclotron resonance. Accordingly, the high energy electrons are easy to be produced, and hence, the negatively charged voltage is easy to increase at the substrate.
Because of the reasons in items 1) and 2), the technique of the related art can insufficiently suppress the charging up of the substrate, surface. Specifically, the capability of suppressing the charged voltage of the substrate surface was approximately xc2x110-12V at most in the technique of the related art.
Recently, there is an increasing demand of more suppressing the charging up of the substrate surface and more reducing the charged voltage.
In manufacturing the semiconductor device by the ion implanting process based on the ion beam irradiation, it is required to keep the charged voltage of the substrate surface at low voltage (e.g., 6V or lower) during the ion implantation is present in order to avoid the insulation breakdown of the semiconductor device, with the recent trend of miniaturizing the semiconductor device structure. However, the device of the related art is almost incapable of satisfying such a requirement.
It is an object of the present invention to suppress the charge-up of the surface of the substrate to a small value at the time of ion beam irradiation where a plasma production device of the radio frequency discharge type is used for ion irradiation apparatus.
An ion irradiation apparatus and a plasma production device for an ion beam irradiation apparatus for irradiating to a substrate an ion beam moved to a moving direction, the plasma production device of the present invention comprises:
a plasma production chamber being elongated along an axis extending in the beam moving direction, the plasma production chamber for producing a plasma by the radio frequency discharge, the plasma production chamber having a couple of holes defined along the axis; and
a magnet disposed outside the plasma production chamber for producing a magnetic field directed along the axis,
wherein the magnetic field bends an ion in the plasma toward the substrate. Since plasma, which is wide and elongated in the ion beam scanning direction, is produced within the plasma production chamber, the wide and long plasma is emitted from the plasma producing chamber through the plasma emission hole by the first magnetic field.
As a result, the plasma is uniformly supplied to a region in the vicinity of the ion beam being moved for scan, so that the charging up occurred on the surface of the substrate is uniformly suppressed by the plasma. The plasma suppresses to produce a large charged voltage, which is locally on the substrate surface. Accordingly, the problem referred to 1) above is successfully solved.
The inventors of the present invention has studied the subject matter and conducted various experiments, and found the following fact. Even if electrons with high energy are included in the plasma produced by the plasma production device, the negative charges in the substrate surface are satisfactorily neutralized by increasing the amount of the ions (referred to as positive ions), which is supplied from the plasma to the substrate. As a result, the charged voltage of the substrate surface can be reduced effectively.
The first magnetic field, which is developed by at least one of the magnets, includes the second magnetic field capable of bending to the substrate ions including in the plasma, which is emitted from the plasma producing chamber. By using the first magnetic field, the ions in the plasma are bent and guided to the substrate, whereby the amount of ions supplied to the substrate may be increased. As a result the negative charges of the substrate surface, caused by the electrons in the plasma emitted from the plasma production device, are satisfactorily neutralized by the ions in the plasma. Moreover, the charge-up of the substrate surface is suppressed, and the charged voltage thereof may be reduced. For this reason, the problem 2) stated above may be solved.
In the present invention, the charge-up of the surface of a substrate is suppressed to a small value at the time of ion beam irradiation by the above-mentioned two operations synergistically, while a plasma production device of the radio frequency discharge type is used. Accordingly, the charged voltage of the substrate surface is reduced to a small value of voltage.
At least one of the magnets is preferably movable in such a directions as to vary its distance to the plasma emission hole. By the movable magnet, an intensity of the second magnetic field to bend the ions to the substrate may be adjusted, and hence, the amount of ions supplied to the substrate may be adjusted. As a result, the balance between the amounts of the positive and negative charges on the substrate surface may be more optimized. Moreover, the charge-up of the substrate surface is suppressed and the charged voltage on the surface may be less.